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Analysis Of Heavy Metals In Canal Sediments To Gain A Better Insight Into Current And Future Canal Management Strategies

Congress: 2015
Author(s): Ian Clark (Nottingham, UK)


Keyword(s): Sub-theme 10: Management of water resources,
Oral:
Abstract*I. Clark, *R. Gomes, *T. H. H. Tran, *V. Archibald, *C. Somerfield *Department of Chemical and Environmental Engineering, The University of Nottingham, United Kingdom Faculty of Engineering, University Park, Nottingham, NG7 2RD Introduction The Birmingham Canal Network (BCN) was once an important industrial route between London and the Midlands. Coal and metal working industries formed along its banks during the industrial revolution leading to contamination the canal system throughout its working years. Nowadays the BCN is primarily used for leisure boating and is maintained by The Canal River Trust along with the other canal networks across the UK. As part of the maintenance of the canals periodic dredging occurs, and the waste is de-watered, blended with non-hazardous materials and finally disposed of in non-hazardous waste landfill sites. This process is neither cost effective nor sustainable but with very little knowledge of what is contained within the waste it is currently the best available practice. The overall aim of the research focussed on identifying heavy metals (As, Cd, Co, Cr, Mn, and Pb) in sediment to confirm whether or not the current canal management strategies are appropriate and if they can be improved with regards to cost effectiveness and sustainability. The first objective of the investigation was to develop a data set that gave an appropriate scale of the contamination of the canal bed by sampling at 5 different locations and at different depths into the bed. Second was to use the data collected to consider potential strategies for better canal management. Smethwick was selected for sampling based on the industrial history of the area and the 5 sampling points (Figure 1) were chosen based on previous industries in different areas along the canal [1]. Materials and Methods Sampling was carried out using two pieces of equipment specifically designed for this investigation; one a coring device and the second an extraction device. Both pieces of equipment ensured the cores remained undisturbed allowing analyses at different depths to be carried out. Samples were digested using aqua regia, or by using a microwave total digestion method. The analysis was completed using a PerkinElmer Optima 3300DV Inductively Coupled Plasma Atomic Emission Spectrometry (ICP-AES) instrument with an auto-sampler (model: AS-90) attached. Results and Discussion The reliability of aqua regia digestion was tested by comparing both aqua regia and total digestion methods on certified reference materials (CRM). The comparison of aqua regia and total digestion of the CRM and samples indicates that not all the target analytes were readily leached from the sediment matrix by aqua regia alone. As and Mn were recovered above 90% in some cases, whereas the recovery of Cr and Pb were ca37-50% and ca30-60% respectively. Robustness of the final dataset was maintained through the duplication of samples at different stages of the sample preparation process. The analysis run also contained a number of quality control standards (QC) and blank solutions which checked for instrumental drift. The data from the blank samples and QCs did not suggest that any drift occurred during the analysis and that the data, for the most part, was reliable. The As data points were consistently above 26 mgkg-1, the lowest concentration found for Cd was 11.3 mgkg-1 and Cr was detected at concentrations above 200 mgkg-1. Lead was identified at concentration of more than 652 mgkg-1. It can also be assumed that the concentrations of Cr and Pb are higher due to the poor recovery efficiency of aqua regia. The EU landfill directive has non-hazardous landfill limits of; 0.4 mgkg-1 0.6 mgkg-1, 4 mgkg-1, 5 mgkg-1 for As, Cd, Cr and Pb respectively [2]. The Cobalt content in the sediment was between 43 and 87 mgkg-1. The Mn content of the canal samples was high at between 828 mgkg-1 and 3415 mgkg-1. Mn and Co are not covered in the landfill directive and are therefore not target elements due to toxicity [2], they are however useful metals in a number of industries. Manganese can be used as an alloy in steel production and the cost of cobalt is 32 000 USD tonne-1 (Oct 2014) [3]. Conclusion The data indicates that the concentration of these elements in the sediment is above the landfill limits for non-hazardous waste, and so the current management practice of is justified. Some form of recovery would be recommended because in some cases the lowest concentration recorded is more than 2 orders of magnitude greater than the landfill limit. Large volumes of inert waste are required for blending to reduce the concentration appropriately. This data set is the start of forming a future canal management strategy that will ideally be sustainable both environmentally and economically. Total digestion and recovery of high value metals appears to be a feasible option for a strategy provided the products can be utilised to offset the cost of the overall canal maintenance. References 1. Baggs, A.P., G.C. Baugh, and D.A. Johnston. Smethwick Econmic History. 1976 [cited 2012 November 20th]; An account of the industrial past of smethwick]. 2. COUNCIL DECISION of 19 December 2002 establishing criteria and procedures for the acceptance of waste at landfills pursuant to Article 16 of and Annex II to Directive 1999/31/EC. Official Journal of the European Communities, 2003: p. 22. 3. London Metal Exchange: Cobalt. 2014 [cited 2013 27/10/2014]; Available from: http://www.lme.com/en-gb/metals/minor-metals/cobalt/.
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